Wrist mechanisms are designed to orient its end effector as demanded by workpiece placement. Wrist mechanisms provide three articulations that offer motions commonly called pitch, yaw and roll. Similar articulations of the arm deliver the wrist assembly anywhere in the robot's sphere of influence. Thereafter it requires three more articulations of the wrist mechanism for universal orientation of the end effector.
Many mechanical wrist mechanisms are multi-axes mechanisms. For example, U.S. Pat. Nos. 3,231,098 and 3,315,542 both disclose such mechanisms. Many of such mechanisms, however, do not provide an unobstructed passageway which provides protection for hoses and wires which respectively provide fuel and power to a work tool mounted on the free end of the wrist mechanism.
U.S. Pat. No. 4,218,166 discloses a multi-axis wrist mechanism which provides independent movement about two axes and which maintains an unobstructed passage between a stationary base and a work tool.
U.S. Pat. No. 4,402,234 to Malarz et al discloses a wrist mechanism having three independent rotational axes which are mutually intersecting. A gearing mechanism controls the independent rotation of components supported for rotation about the three axes and also provides an unobstructed internal passageway for housing hoses and/or wires. The use of such a wrist mechanism, however, is somewhat limited and/or difficult due to the relatively small internal bend radius of the wrist mechanism. This imposes limitations on the amount of rotational movement that the housed hoses and wires will permit. Such a small bend radius furthermore makes programming of the robot to which the wrist mechanism is attached more difficult. This occurs because the freedom of movement of the wrist mechanism is limited which the programmer must take into consideration.
Other U.S. patents which disclose wrist mechanisms of lesser relevance include U.S. Pat. Nos. Re. 25,889; 2,514,250; 2,861,700; 2,871,701; 3,043,448; 3,066,805; 3,108,498; 3,182,813; 3,784,031; 4,001,556; 4,068,536; 4,099,409; 4,149,278; 4,353,677; 4,356,554; 4,365,928; 4,370,836 and 4,392,776.